There have conventionally been proposed many cookers or ovens that use high-temperature gas such as hot air or steam. Examples of such a conventional cooker are disclosed in Patent Publications 1 to 4. Patent Publication 1 discloses a steam cooking apparatus that injects steam into a food tray. Patent Publication 2 discloses a cooking apparatus that sends superheated steam into an oven chamber, or converts steam inside the oven chamber to superheated steam through radiation heating. Patent Publications 3 and 4 disclose steam convection ovens that can cook foods with steam as well as with heat.    Patent Publication 1: JP-U-03-67902 (pp. 4 to 6 in the entire specification, FIGS. 1 to 3)    Patent Publication 2: JP-A-08-49854 (pp. 2 to 3, FIG. 1, FIGS. 2 to 8)    Patent Publication 3: JP-A-09-89260 (pp. 2 to 3, FIGS. 1 to 3)    Patent Publication 4: JP-A-09-105524 (pp. 2 to 3, FIGS. 1 to 3)